As is known such a speed change device generally comprises a driving pulley, a driven pulley and an endless transmission belt looped over the pulleys. Each of the pulleys comprises a hub, two annular plates or pulley sides facing each other and disposed around the associated hub. At least one of the pulley sides is called a movable pulley side is axially movably mounted on the associated hub under the bias of axially acting resilient return means.
The present invention is more particularly directed to the case in which such axially acting resilient return means includes an annular diaphragm spring which rockably axially bears at its outer periphery against the movable pulley side and rockably axially bears through radial fingers spaced by slots in the central portion of the diaphragm spring, against an abutment member axially fixed relative to the hub.
Such a speed change device is disclosed in U.S. Pat. No. 4,132,120 and in copending application U.S. Ser. No. 610,512 filed May 15, 1984, now U.S. Pat. No. 4,573,948 and assigned to the assignees of the instant application.
In practice the movable pulley side of the driving and driven pulleys are mutually displaceable between advanced and retracted endmost positions. When the movable plate of the driving pulley is in its advanced position the movable pulley of the driven pulley is in its retracted position and vice versa, and for each of the positions of the movable pulley side the belt has a predetermined position which corresponds to the transmission ratio. For example, in the rest position the movable pulley side of the driving pulley may be in the advanced position and the movable pulley side of the driven pulley will be in the retracted position, the transmission ratio will then be at its highest. Conversely, in operation, if under the action of suitable control means the movable side of the driving pulley is displaced from its advanced position to its retracted positon the movable side of the driven pulley is displaced in the opposite direction from its retracted position to its advanced position, the transmission ratio will be reduced accordingly.
In any event, as regards the driving pulley the movable side is constantly urged toward the advanced position by the associated axially acting resilient return means and the resilient return means returns the movable side from its retracted position to its advanced position.
It has been established that at least in such applications the diaphragm spring usually employed is inadequate to satisfactorily return the movable side of the pulley. It has been proposed to add additional resilient means comprising one or more coil springs coaxially disposed with respect to each other bearing against a shoulder axially fixed to the movable side.
Whereas an axially bearing surface for the radially inner coil spring may be relatively easily found directly on the abutment member through the central opening in the diaphragm spring such is not the case for the radially outer coil spring unless the central opening in the diaphragm spring is enlarged which for a given diameter of the diaphragm spring would reduce the effective size of the diaphragm spring to the detriment of its operating characteristics.
It therefore was contemplated to have the radially outer coil spring bear against an annulus disposed on the side of the diapharagm spring remote from the abutment member and fixed axially relative to the abutment member by means of a sleeve extending axially through the central opening of the diaphragm spring at the expense of a considerable complication of the device or have the radially outer coil spring bear against the abutment member through the diaphragm spring itself, and more particularly the central portion of the diaphragm spring.
But aside from the fact that the radially outer coil spring is not well seated, such an arrangement brings a first metal part, i.e., the diaphragm spring, in contact with another metal part with respect to which it is relatively movable, namely rocking movement, thereby producing friction and wear between the metal parts and at the same time a risk of binding by fusion welding the metal parts together and a risk of throwing the outer coil spring off center.